This invention relates to methods of manufacturing an electronic device comprising at least one semiconductor device (for example a thin-film transistor) which has a body portion of semiconductive crystalline silicon material formed by annealing with an energy beam, and further relates to devices manufactured by such methods. The invention relates particularly but not exclusively to the manufacture of electronic devices wherein the semiconductor devices provide circuitry for driving an array of switching devices formed on the same substrate as the semiconductor devices. Such switching devices may be of the MIM-type, and the electronic device may be, for example, a liquid-crystal display or a data store.
For very many years amorphous-silicon thin-film transistors (TFTs) were used as the switching devices in an array for actively controlling the operation of the picture elements of a liquid-crystal display. In more recent years MIM-type devices have been used instead of thin-film transistors, because the MIM-type devices have only two terminal electrodes and are comparatively simple to manufacture.
A MIM type device is a type of switching diode having a non-linear current-voltage characteristic through one or more layers of insulating material between two metallic (i.e. conductive) layers which form the diode electrodes. Hence the acronym "MIM" is derived from the English "Metallic-Insulative-Metallic". Published United Kingdom patent applications GB-A-2 213 987 and U.S. Pat. No. 5,236,573, and published European patent applications EP-A-0 182 484, EP-A-0 202 092 and EP-A-0 333 392 describe the fabrication of MIM-type diodes with non-stoichiometric silicon-based compounds, for example silicon nitride, silicon oxide, silicon oxynitride and/or silicon carbide as the insulative material, and further describe their use as switching devices in arrays for the active matrix addressing of a liquid-crystal display. The MIM-type diodes in the array are switched on by applying sequentially a moderately high scanning voltage signal (for example in the range of 10 to 15 volts) to row conductors of the display. The whole contents of GB-A-2 213 987, GB-A-2 231 200, EP-A-0 182 484, EP-A-0 202 092, and EP-A-0 333 392 are hereby incorporated herein as reference material.
Preferably the driving circuitry for addressing such an array is integrated on the same substrate as the array so as to reduce the number of external connections. Typically the substrate is of a low-cost material such as a glass or plastics material, and so only low-temperature processing steps should be used to fabricate the driving circuitry. Therefore preferably the semiconductor device technology used to fabricate the driving circuitry should not involve heating the substrate (at least for any significant time) to temperatures above, for example, about 700.degree. C.
When the switching array is formed of thin-film transistors, the driving circuitry can also be formed of thin-film transistors integrated on the display substrate(s). Thus, row drivers may be formed with thin film transistors having a sufficiently high mobility to allow the row conductors to be scanned at, for example, about 30 kHz for a television display device. In simple terms, the field-effect mobility needs to be in excess of about 1 cm.sup.2.V.sup.-1.s.sup.-1 to achieve this scanning rate, and this high mobility can be achieved in crystalline silicon material formed by depositing a layer on a substrate and annealing at least a part of the layer with an energy beam. Specific examples using a CW argon laser beam are described in the articles "High-voltage polysilicon TFTs with multi-channel structure" by T. Unagami in IEEE Transactions on Electron Devices Vol. 35 No. 12, December 1988, pages 2363 to 2367, "Low Temperature Fabrication of Poly-Si TFT by Laser Induced Crystallization of a-Si" by Masumo et. al. in Journal of Non-Crystalline Solids Vol. 115 (1989) pages 147 to 149, and "A laser-recrystallization technique for silicon-TFT integrated circuits on quartz substrates, and its application to small-size monolithic active-matrix LCDs" by E. Fujii et. al. in IEEE Transactions on Electron Devices Vol. 37 No. 1, January 1990, pages 121 to 127. The whole contents of all these articles are hereby incorporated herein as reference material. In this known laser-annealed device process technology, the deposited layer is of semiconductive amorphous or small-grain silicon and is annealed into large-grain polycrystalline silicon (polysilicon) by heating with the laser beam. This technology provides satisfactory TFTs to form the driving circuitry of the TFT switching array.
However, the driving circuits for a MIM device array cannot be fabricated as MIM-type devices, and so a different device technology with different materials is required on the substrate when the switching array is formed of MIM-type devices.